History, I've been reading this forum for quite some time and it has enlightened me on several occasions. However, I felt the need to "chime-in" on this doorbell issue. I'm a licensed electrician, in Arkansas BTW, and teach an electrical systems apprentice course. So I feel qualified to input my opinion on this matter, maybe it will help. Took a few minutes to look up "why" this is wrong. So let's begin. First, that keyless lampholder (note lampholder not fuseholder) is NOT listed (see UL Whitebook) as a fuseholder. The two applications are way different. This I promise. Second (going with the 2005 NEC as my 2008 is at work), Art 250.51(B) Edison base fuses are for replacement only. That means, not for new construction. Third, Art. 240.30(A) talks about physical protection with fuses in an enclosure. and 240.41 discussed their location. Fourth, Art. 240.52 means Edison base fuseholder must be able to accept Type S plug fuses; not to mention that Art. 725 has a plethora of information regarding low voltage installations that would be beneficial with this situation. Bottom line is that this setup is wrong albeit that's the way it's been done for 30 years. Electricians probably shouldn't be installing 1920's era overcurrent protection anyway and NEC prevents that with plug fuses. I would have it repaired as it's looks like a crummy install anyway. Hang the bell transformer off to the side of the box via a knockout, the 120V lines inside the box with a cover, the low voltage lines (usually 16V) stay outside. The branch circuit overcurrent protection will more than suffice for the protection of the conductors during faults as long as the circuit has the necessary equipment grounding. One other note of interest, if every little piece of electrical equipment needed protection at such a level, based on the equipment's wire size, then every single light fixture (luminaries) in your house should have little fuses placed in them. There is an article discussing the overcurrent protection for small fixture wires as well. There ya have it. Hope this helps.